Conventionally, a gear shift control apparatus for a vehicular transmission equipped with a sub transmission is known which performs a synchronization gear-shift such that a speed (gear) ratio of the variator to meet with the gear ratio of the sub transmission so that a whole gear ratio of a whole of the transmission is met with a target value (the gear ratio of the whole of the transmission is hereinafter called a through gear ratio) during a time at which a gear-shift request (demand) occurs (for example, refer to a Patent Document 1).
Incidentally, it is considered that, during a vehicular stop, a 2-1 speed gear-shift is carried out without carrying out a gear-shift (so-called, 2-1 (speed) gear-shift) of the sub transmission from a 2-nd speed gear stage to a 1-st speed gear stage during a vehicular deceleration. The reasons of the above-described not carrying out the gear-shift during the deceleration are two points as will be described below.
That is, as a first point, an avoidance of a shock occurring during the traveling in association with the gear-shift (a clutch-clutch replacement gear shift).
As a second point, the avoidance of the variator from not being returned to a lowest gear ratio (the variator is up-shifted due to the synchronization gear-shift in association with the 2-1 speed gear-shift of the sub transmission). The variator is down-shifted toward the lowest gear ratio when the 2-1 speed gear-shift of the sub transmission is ended. For example, during an abrupt deceleration, the vehicle is often stopped without the completion of the gear-shift to the lowest gear ratio.)
In this way, in the transmission having the variator and the sub transmission disposed in series with the variator, the structure in which the sub transmission carries out the 2-1 speed gear-shift when the vehicle is started in the stopped state brings such a problem as will be described below. That is, in a case where a time duration during the vehicular stopped state is short, there is a possibility that a driving force is insufficient when the vehicle is started.
That is, at a timing at which the vehicle is stopped, the vehicle is swung in a forward-and-backward direction due to a swing back of the vehicle. Even when a vehicle speed indicates zero, the vehicle is not determined to be stopped (but is determined to be stopped after a passage of a determination time from zero vehicle speed). Hence, the 2-1 speed gear-shift of the sub transmission is not started. When the vehicle is tried to be started in this state, the sub transmission is left at the 2-nd speed, the driving force of the 1-st speed cannot be obtained so that, when the vehicle is started, there is a probability of being insufficient driving force. For example, this is easy to occur when a vehicle driver stops the vehicle at an entrance of a high-way road. Specifically, the vehicle driver decelerates the vehicle in order to receive a traffic ticket with the vehicle stopped in front of a ticketing machine and then often starts the vehicle. In this case, although the vehicle speed is temporarily zeroed, in a stop determination, the determination that the vehicle is stopped is not made and the sub transmission is left at 2-nd speed (stage). It can be thought that the sub transmission is forced to perform the 2-1 speed gear-shift on a basis of the vehicle start request. However, during the gear-shift, a 1-st speed driving force cannot be obtained and it is unavoidable that the driving force is insufficient when the vehicle is started.